Tuyere for Manufacturing Molten Iron and Method for Injecting Gas Using the Same

ABSTRACT

A tuyere for manufacturing molten iron is provided. The tuyere includes i) an oxygen injection opening that is configured to inject oxygen therethrough, and ii) a sealing gas injection opening that is located to be spaced apart from the oxygen injection opening and is configured to inject a sealing gas surrounding the oxygen.

TECHNICAL FIELD

This application claims priority to and the benefit of Korean Patent Application Nos. 2007-0087315 and 2007-0136401 filed on Oct. 29, 2007 and Dec. 24, 2007, respectively, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

The present invention relates to a tuyere for manufacturing molten iron and a method for injecting gas using the same, and more particularly to a tuyere that is capable of being prevented from being melted and consequently damaged by charged materials in a melter-gasifier, and a method for injecting gas using the same.

BACKGROUND ART

Since a blast furnace method for manufacturing molten iron has many problems such as an environmental pollution, a smelting reduction process, which can replace the blast furnace method, has been researched. In the smelting reduction process, raw coal is directly used as a fuel and a reducing agent and an iron ore is directly used as an iron source. The iron ore and the raw coal are charged into the melter-gasifier and then the iron ore is melted to be manufactured into molten iron.

A tuyere is installed at a side portion of the melter-gasifier and oxygen is injected into the melter-gasifier through the tuyere. The oxygen injected into the melter-gasifier combusts a char bed formed in the melter-gasifier. Therefore, the iron ore charged into the melter-gasifier is melted by combustion heat, and thereby the molten iron is manufactured.

DISCLOSURE Technical Problem

A tuyere that is capable of being prevented from being melted and consequently damaged by using a sealing gas is provided. In addition, a method for injecting gas using the above-described tuyere is provided.

Technical Solution

A tuyere according to an embodiment of the present invention is used for manufacturing molten iron. The tuyere includes i) an oxygen injection opening that is configured to inject oxygen therethrough, and a sealing gas injection opening that is spaced apart from the oxygen injecting opening and is configured to inject a sealing gas surrounding the oxygen.

The tuyere may further include i) a first end portion through which the oxygen injection opening is exposed, and a second end portion that surrounds the first end portion. The sealing gas injection opening is exposed through the second end portion. The first end portion may have a concave groove.

The sealing gas injection opening may include a plurality of nozzles through which the sealing gas is injected. The plurality of nozzles may be spaced apart from each other at substantially equal intervals.

The sealing gas injection opening may further include i) a sealing gas supply tube to which the sealing gas is supplied, and a sealing gas header that is connected to the plurality of nozzles and the sealing gas supply tube with each other. The sealing gas supply tube may be extended along one direction. The sealing gas header may be formed to have a ring shape.

The tuyere according to an embodiment of the present invention may further include an auxiliary fuel injection opening that is spaced apart from the oxygen injection opening. An auxiliary fuel may be injected through the auxiliary fuel injection opening. The oxygen injection opening may be located between the sealing gas injection opening and the auxiliary fuel injection opening.

One or more nozzles among the plurality of nozzles may be formed to be extended to make an acute angle with a direction along which the oxygen injection opening is extended. The acute angle may be in a range from 5 degrees to 60 degrees. A cross-section of the nozzle cut along a width direction of the tuyere may become larger while becoming closer to the second end portion.

The oxygen injected through the oxygen injection opening and the sealing gas injected through the sealing gas injection opening may make an acute angle. The acute angle may be in a range of 5 degrees to 60 degrees.

The tuyere according to an embodiment of the present invention may further include an auxiliary fuel injection opening that is spaced apart from the oxygen injection opening. An auxiliary fuel is injected through the auxiliary fuel injection opening. The auxiliary fuel may be a fine carbonaceous material or a hydrocarbon-containing gas.

The tuyere may further include i) a first end portion at which the oxygen injection portion is formed, and a second end portion at which the sealing gas injection opening is formed and surrounding the first end portion. Therefore, the first end portion and the second end portion may be located at the same plane.

The sealing gas may be at least one gas selected from a group of compressed air, oxygen with a low concentration and an insert gas. The inert gas may be nitrogen gas if the sealing gas may include the inert gas. The tuyere may be installed at a side portion of the melter-gasifier that manufactures molten iron such that the sealing gas prevents charged materials in the melter-gasifier from reacting with the oxygen at an end portion of the tuyere.

A method for injecting gas according to an embodiment of the present invention includes i) injecting oxygen into the melter-gasifier through the tuyere installed at the melter-gasifier, injecting sealing gas into the melter-gasifier through the tuyere, and surrounding the oxygen by the sealing gas while the sealing gas is injected into the melter-gasifier.

A method for injecting gas according to an embodiment of the present invention may further include preventing the charged materials in the melter-gasifier from reacting with the oxygen by the sealing gas. The sealing gas may be injected to make an acute angle with the oxygen during the injection of the sealing gas. The acute angle is in a range of 5 degrees to 60 degrees.

A method for injecting gas according to an embodiment of the present invention may further include injecting an auxiliary fuel into the melter-gasifier through the tuyere. The auxiliary fuel may be a fine carbonaceous material or a hydrocarbon-containing gas.

The sealing gas may be at least one gas selected from a group of compressed air, oxygen with a low concentration, and an insert gas during the injection of the sealing gas. The inert gas may be nitrogen gas if the sealing gas includes the inert gas.

ADVANTAGEOUS EFFECTS

Since the tuyere can be prevented from being melted and consequently damaged, longevity of the tuyere can be significantly increased and a process for manufacturing molten iron can be stably carried out.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic perspective view of the tuyere according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of the tuyere cut along the line II-II of FIG. 1.

FIG. 3 is a schematic view showing an operating state of the tuyere of FIG. 1.

FIG. 4 is a schematic cross-sectional view of the tuyere according to a second embodiment of the present invention.

FIG. 5 is a schematic view showing a melter-gasifier installed with a tuyere of FIG. 4.

FIG. 6 is a simulated photograph of a tuyere according to a first exemplary example of the present invention.

FIG. 7 is a simulated photograph of a tuyere according to a second exemplary example of the present invention.

BEST MODE

It will be understood that, although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context dearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including”, when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.

All terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

The embodiments of the present invention will be explained in detail with reference to FIGS. 1 to 5 below. These embodiments are merely to illustrate the present invention and the present invention is not limited thereto.

FIG. 1 is a schematic perspective view of a tuyere 10 according to a first embodiment of the present invention. A structure of the tuyere 10 shown in FIG. 1 is merely to illustrate the present invention, and the present invention is not limited thereto. Therefore, a structure of the tuyere 10 can be modified in other forms.

The tuyere 10 shown in FIG. 1 is used for manufacturing molten iron. Therefore, the tuyere 10 is installed at a side portion of a melter-gasifier 50 (shown in FIG. 5, the same hereinafter), thereby supplying oxygen to the melter-gasifier 50. The oxygen is injected into the melter-gasifier 50 and then combusts coal that has been charged into the melter-gasifier 50, and thereby molten iron can be manufactured.

As shown in FIG. 1, an end portion 105 of the tuyere 10 includes a first end portion 1051 and a second end portion 1053. The first end portion 1051 is formed with a concave groove. Therefore, the second end portion 1053 is protruded to be closer to the melter-gasifier 50 than the first end portion 1051 when the tuyere 10 is installed at the melter-gasifier 50.

The second end portion 1053 surrounds the first end portion 1051. A sealing gas injection opening 103 is exposed through the second end portion 1053. A plurality of nozzles are formed in the second end portion 1053.

Meanwhile, as shown in FIG. 1, the tuyere 10 includes an oxygen injection opening 101 and the sealing gas injection opening 103. The oxygen is injected through the oxygen injection opening 101. Here, the oxygen includes not only pure oxygen but also a gas containing oxygen. The oxygen injection opening 101 includes an oxygen supply line 1011 and the oxygen is supplied therefrom.

The sealing gas injection opening 103 is located to be spaced apart from the oxygen injection opening 101. The sealing gas is injected through the sealing gas injection opening 103 while surrounding the oxygen gas. Therefore, the end portion 105 can be sealed by the sealing gas. That is, the end portion 105 can be prevented from being damaged to contact the charged materials in the melter-gasifier 50 by using the sealing gas. An inert gas atmosphere is formed to suppress the charged materials from being recombusted or from generating an oxidization reaction even if the charged materials contact oxygen.

The sealing gas injection opening 103 includes a sealing gas supply line 1035 and a plurality of nozzles 1031. The sealing gas supply line 1035 supplies the sealing gas. The supplied sealing gas is injected into the melter-gasifier 50 through the plurality of nozzles 1031. The plurality of nozzles 1031 are arranged to be spaced apart from each other at substantially equal intervals. Therefore, since the sealing gas can be uniformly injected into the melter-gasifier 50, sealing efficiency can be optimized.

Here, the sealing gas may be compressed air, oxygen with a low concentration, or an inert gas. If the sealing gas is compressed air, the concentration of oxygen cannot be more than 30 vol %. In addition, the sealing gas may be an inert gas itself or a gas including the inert gas. For example, nitrogen and so on can be used as the inert gas. Since a large amount of nitrogen exists in air, it is most suitable to be used. The sealing gas suppresses the oxygen from reacting with the charged materials in the melter-gasifier 50 by surrounding the oxygen. Therefore, the end portion 105 is prevented from being melted and consequently damaged by high heat that is generated by reaction between the charged materials and oxygen.

As shown in FIG. 1, the tuyere 10 is connected to end portion cooling tubes 1071 and 1073 and body cooling tubes 1091 and 1093. Cooling water cools the end portion 105 of the tuyere 10 while entering into and being discharged from the end portion cooling tubes 1071 and 1073. The cooling water enters into the end portion 105 through the cooling water inlet tube 1071. After the cooling water cools the end portion 105, it is discharged outside through the cooling water outlet tube 1073.

Meanwhile, more cooling water enters into the body of the tuyere 10 along a direction indicated by an arrow through the cooling water inlet tube 1091. After the cooling water cools the body of the tuyere 10, it is discharged outside through the cooling water outlet tube 1093. A cooling structure of the tuyere 10 will be explained in detail below with reference to FIG. 2.

FIG. 2 schematically shows a cross-sectional structure of the tuyere 10 cut along a line II-II of FIG. 1. The end portion cooling tubes 1071 and 1073 and the body cooling tubes 1091 and 1093 of FIG. 1 are omitted in FIG. 2 for convenience.

As shown in FIG. 2, the tuyere 10 includes the end portion cooling chamber 107 and the body cooling chamber 109. The end portion cooling tubes 1071 and 1073 (shown in FIG. 1) are connected to the end portion cooling chamber 107 while the body cooling tubes 1091 and 1093 (shown in FIG. 1) are connected to the body cooling chamber 109. The cooling chambers are divided into the end portion cooling chamber 107 and the body cooling chamber 109. Since the end portion cooling chamber 107 and the body cooling chamber 109 are independently cooled, the body of the tuyere 10 can be continuously cooled even if the end portion 105 of the tuyere 10 is damaged to expose the end portion cooling chamber 107. As a result, after the cooling water flowing into the end portion cooling chamber 107 is blocked, a process for manufacturing molten iron can be continuously carried out.

As shown in FIG. 2, the sealing gas injection opening 103 includes the nozzles 1031, a sealing gas header 1033, and the sealing gas supply tube 1035. In addition, the sealing gas injection opening 103 may further include other components.

As shown in FIG. 2, the nozzle 1031 is formed to make acute angles θ₁ and θ₂ with a direction (X-axis direction, indicated by a dotted line) along which the oxygen injection opening 101 is extended. Therefore, the sealing gas injected through the nozzle 1031 surrounds the oxygen injected through the oxygen injection opening 101. Here, the acute angle θ₁ or θ₂ can be in a range of 5 degrees to 60 degrees. If the acute angle θ₁ or θ₂ is less than 5 degrees, a sealing effect cannot be expected since injection directions of the oxygen and sealing gas are almost parallel. On the contrary, if the acute angle θ₁ or θ₂ is over 60 degrees, the oxygen cannot be injected well toward +X-axis direction since the sealing gas is injected to be very close to the end portion 105.

Meanwhile, as shown in FIG. 2, a cross-section 1033 s that is formed by cutting the nozzle 1031 along the X-axis direction, that is, a width direction of the tuyere 10, is becomes larger as the nozzle 1031 becomes close to the second end portion 1053. Therefore, the sealing effect can be maximized since the sealing gas can be injected as a form of a curtain with a predetermined width.

The sealing gas header 1033 connects the plurality of nozzles 1031 and the sealing gas supply tube 1035 with each other. The sealing gas header 1033 is formed to have a ring shape. Therefore, the sealing gas header 1033 receives the sealing gas supplied from the sealing gas supply tube 1035 extended along one direction and distributes it as a ring shape. The sealing gas that is dispersed as a ring shape in the sealing gas header 1033 can be uniformly injected outside through the plurality of nozzles 1031.

FIG. 3 schematically shows an operating state of the tuyere 10 of FIG. 1. As shown in FIG. 3, the tuyere 10 is installed at a side portion of the melter-gasifier 50, thereby injecting oxygen into the melter-gasifier 50.

As shown in FIG. 3, the oxygen is injected through the oxygen injection opening 101 while the sealing gas is injected to surround the oxygen through the sealing gas injection opening 103. The oxygen is injected into the melter-gasifier 50, thereby combusting the char bed and forming a raceway.

Meanwhile, as indicated by an arrow, a backflow is formed by the charged materials in the melter-gasifier 50. The charged materials in the melter-gasifier 50 are not re-combusted or oxidized since they do not contact the end portion 105 of the tuyere 10 and the oxygen by the sealing gas. Here, the charged material can be non-combusted coal, slag, or molten iron.

The sealing gas prevents the charged materials from reacting with the oxygen at the end portion 105. In addition, the sealing gas pulls the charged materials while being collected in front of the oxygen injection opening 101 by a backflow characteristic of the charged materials and forming a non-combustion atmosphere. Therefore, the charged materials are not re-combusted or oxidized in front of the oxygen injection opening 101.

As shown in FIG. 3, the oxygen and the sealing gas are injected into the melter-gasifier 50 to form an acute angle θ₃ or θ₄. The acute angle θ₃ or θ₄ may be in a range of 5 degrees to 60 degrees. If the acute angle θ₃ or θ₄ is less than 5 degrees, the oxygen and the sealing gas are injected to be in an almost parallel manner with each other. Therefore, it is impossible to expect a sealing effect. On the contrary, if the acute angle θ₃ or θ₄ is over 60 degrees, the oxygen may not be injected well from the oxygen injection opening 161 due to the sealing gas.

FIG. 4 schematically shows a cross-sectional structure of a tuyere 20 according to a second embodiment of the present invention. Since the structure of the tuyere of FIG. 4 is similar to that of the tuyere 10 of FIG. 2, like elements are referred to by like reference numerals and detailed descriptions thereof are omitted.

As shown in FIG. 4, the tuyere 20 further includes an auxiliary fuel injection opening 201. The auxiliary fuel injection opening 201 is spaced apart from the oxygen injection opening 101 and injects an auxiliary fuel. The oxygen injection opening 101 is located between the auxiliary fuel injection opening 201 and a sealing gas injection opening 203. Therefore, a space for installing the auxiliary fuel injection opening 201 and the sealing gas injection opening 203 together can be secured in the tuyere 20 by not arranging the auxiliary fuel injection opening 201 and the sealing gas injection opening 203 together.

For example, a fine carbonaceous material, a hydrocarbon-containing gas, and so on can be used as the auxiliary fuel. The fine carbonaceous material means a particle containing carbon with a grain size not more than about 3 mm. For example, the hydrocarbon-containing gas can be liquid natural gas (LNG), liquid propane gas (LPG), coke oven gas (COG), and so on. A fuel ratio can be reduced by injecting the auxiliary fuel into the melter-gasifier 50 through the auxiliary fuel injection opening 201.

The auxiliary fuel is injected into the melter-gasifier and thereby increases combustion heat. Therefore, an amount of coal charged from an upper side of the melter-gasifier 50 can be reduced. In addition, the iron ore can be reduced well since the auxiliary fuel generates a large amount of reducing gas. Furthermore, a state of a lower side of the melter-gasifier 50 may be unsuitable for manufacturing molten iron since the coal charged from the upper side of the melter-gasifier 50 may be gasified to disappear before reaching the lower side of the melter-gasifier 50. Therefore, the state of the lower side of the melter-gasifier 50 can be improved by injecting the auxiliary fuel into the lower side of the melter-gasifier 50.

Meanwhile, as shown in FIG. 4, an end portion 205 of the tuyere 20 includes a first end portion 2051 and a second end portion 2053. The oxygen injection opening 101 is formed at the first end portion 2051 while the sealing gas injection opening 203 is formed at the second end portion 2053. Here, the first end portion 2051 and the second end portion 2053 are located on the same plane P. The end portion 205 of the tuyere 20 can be sealed by the sealing gas at the tuyere 20 with the above-described structure.

FIG. 5 schematically shows the melter-gasifier 50 at which the tuyere 20 of FIG. 4 is installed.

As shown in FIG. 5, iron ore and coal are charged into an upper portion of the melter-gasifier 50, and thereby molten iron is manufactured in the melter-gasifier 50 and is then discharged outside. Here, the iron ore may be charged as reduced iron, while the coal may be charged as coal briquettes. The coal briquettes are charged into the melter-gasifier 50 to form a char bed (shown in FIG. 4, the same hereafter) and reducing gas is generated to be discharged outside. The char bed is combusted by oxygen that is injected through the tuyere 20 and combustion heat is then generated. The reduced iron is melted by the combustion heat, thereby manufacturing molten iron. The reducing gas discharged from the melter-gasifier 50 enters into a fluidized-bed reduction reactor or a packed-bed reduction reactor, thereby reducing the iron ore charged thereinto to manufacture reduced iron, respectively.

As shown in FIG. 5, the oxygen, the sealing gas, and the auxiliary fuel are charged into the melter-gasifier 50 through the tuyere 20. Therefore, the combustion heat in the melter-gasifier 50 is increased, and thereby an amount of coal charged from the upper portion of the melter-gasifier 50 can be reduced.

The present invention will be explained in detail below with reference to exemplary examples. The exemplary examples are merely to illustrate the present invention, and the present invention is not limited thereto.

Exemplary Example 1

A flow of sealing gas injected through the tuyere with a structure shown in FIG. 4 was simulated. The diameter of the oxygen injection opening was 34 mm, and nitrogen was used as the sealing gas. The flow amount of the nitrogen was 32 Nm³/hr and injection speed thereof was 40 m/s.

FIG. 6 shows the simulated flow of the sealing gas as lines.

As shown in FIG. 6, the sealing gas injected from the nozzle flowed toward the first end portion while surrounding the oxygen that is injected at a high temperature at a lower portion. That is, the end portion can be effectively sealed since the sealing gas spirally flows.

Exemplary Example 2

A flow of sealing gas injected through the tuyere with a structure shown in FIG. 4 was simulated. The flow amount of the nitrogen was 37 Nm³/hr. A detailed description of the exemplary conditions is omitted since remaining exemplary conditions are the same as those of Exemplary Example 1.

FIG. 7 shows the simulated flow of the sealing gas as lines.

As shown in FIG. 7, the sealing gas injected from the nozzle flowed toward the oxygen while surrounding the oxygen that is injected at a lower portion. Therefore, the end portion can be effectively sealed.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. 

1. A tuyere that is used for manufacturing molten iron, the tuyere comprising: an oxygen injection opening that is configured to inject oxygen therethrough; and a sealing gas injection opening that is spaced apart from the oxygen injecting opening and is configured to inject a sealing gas surrounding the oxygen.
 2. The tuyere of claim 1, wherein the tuyere further comprises: a first end portion through which the oxygen injection opening is exposed; and a second end portion through which the sealing gas injection opening is exposed and surrounding the first end portion.
 3. The tuyere of claim 2, wherein the first end portion is shaped to have a concave groove.
 4. The tuyere of claim 2, wherein the sealing gas injection opening comprises a plurality of nozzles through which the sealing gas is injected.
 5. The tuyere of claim 4, wherein the plurality of nozzles are spaced apart from each other at substantially equal intervals.
 6. The tuyere of claim 4, wherein the sealing gas injection opening further comprises: a sealing gas supply tube to which the sealing gas is supplied, the sealing gas supply tube being extended along one direction; and a sealing gas header connecting the plurality of nozzles and the sealing gas supply tube with each other.
 7. The tuyere of claim 6, wherein the sealing gas header is formed to have a ring shape.
 8. The tuyere of claim 6, further comprising an auxiliary fuel injection opening that is spaced apart from the oxygen injection opening and through which an auxiliary fuel is injected, and wherein the oxygen injection opening is located between the sealing gas injection opening and the auxiliary fuel injection opening.
 9. The tuyere of claim 4, wherein one or more nozzles among the plurality of nozzles is formed to be extended to make an acute angle with a direction along which the oxygen injection opening is extended.
 10. The tuyere of claim 9, wherein the acute angle is in a range from 5 degrees to 60 degrees.
 11. The tuyere of claim 4, wherein a cross-section of the nozzle cut along a width direction of the tuyere becomes larger when becoming closer to the second end portion.
 12. The tuyere of claim 1, wherein the oxygen injected through the oxygen injection opening and the sealing gas injected through the sealing gas injection opening make an acute angle.
 13. The tuyere of claim 12, wherein the acute angle is in a range of 5 degrees to 60 degrees.
 14. The tuyere of claim 1, further comprising an auxiliary fuel injection opening through which an auxiliary fuel is injected and that is located to be spaced apart from the oxygen injection opening.
 15. The tuyere of claim 14, wherein the auxiliary fuel is a fine carbonaceous material or a hydrocarbon-containing gas.
 16. The tuyere of claim 1, wherein the tuyere further comprises: a first end portion at which the oxygen injection portion is formed; and a second end portion that surrounds the first end portion, and at which the sealing gas injection opening is formed, wherein the first end portion and the second end portion are located at the same plane.
 17. The tuyere of claim 1, wherein the sealing gas is at least one gas selected from a group of compressed air, oxygen with a low concentration, and an inert gas.
 18. The tuyere of claim 17, wherein the inert gas is nitrogen gas if the sealing gas comprises the inert gas.
 19. The tuyere of claim 1, wherein the tuyere is installed at a side portion of a melter-gasifier that manufactures molten iron such that the sealing gas prevents charged materials in the melter-gasifier from reacting with the oxygen at an end portion of the tuyere.
 20. A method for injecting gas, comprising: injecting oxygen into a melter-gasifier through a tuyere installed at the melter-gasifier; injecting sealing gas into the melter-gasifier through the tuyere; and surrounding the oxygen with the sealing gas while the sealing gas is injected into the melter-gasifier.
 21. The method of claim 20 further comprising preventing the charged materials in the melter-gasifier from reacting with the oxygen by the sealing gas.
 22. The method of claim 20, wherein the sealing gas is injected to make an acute angle with the oxygen during the injection of the sealing gas.
 23. The method of claim 22, wherein the acute angle is in a range of 5 degrees to 60 degrees.
 24. The method of claim 20 further comprising injecting an auxiliary fuel into the melter-gasifier through the tuyere.
 25. The method of claim 24, wherein the auxiliary fuel is a fine carbonaceous material or hydrocarbon containing gas.
 26. The method of claim 20, wherein the sealing gas is at least one gas selected from a group of compressed air, oxygen with a low concentration, and an inert gas during the injection of the sealing gas.
 27. The method of claim 26, wherein the inert gas is nitrogen gas if the sealing gas comprises the inert gas. 